Video has an aspect ratio, which defines its intended display shape. Typical aspect ratios are 16:9, which is a wide, rectangular format and 4:3, which is narrower. When video is displayed on a device, or in a user interface window, which does not match the aspect ratio, padding or stretching occurs. In the first case, black bars are added to the picture to maintain the picture aspect ratio, while filling the remaining areas of the display. In the second case, the picture is deformed, which is undesirable and usually to be avoided.
Some display implementations constrain the shape of the playback window to the aspect ratio of the video, or otherwise make no effort to provide the user with an indication of the optimal window size. Other display implementations constrain the shape of the playback window to the aspect ratio setting of the device.
Resizable windows, such as those used in MICROSOFT WINDOWS™, or APPLE OSX™, afford the user the ability to resize windows to any shape. While this provides the user with maximum flexibility in screen layout, it often makes it difficult for the user to find the window size which best matches the video aspect ratio. This makes it difficult to eliminate all black bars (or video deformation if stretching is occurring), and to minimize wasted space on a screen.